arm64: dts: mt2712: add ethernet device node

[ Upstream commit e9cabfd046d55d05f11d05fccc4019aa4bad29c6 ]

This patch add device node for mt2712 ethernet.

Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Stable-dep-of: 3baac7291eff ("arm64: dts: mediatek: mt2712: fix validation errors")
Signed-off-by: Sasha Levin <sashal@kernel.org>